Radiation therapy can be used to treat localized cancer. In a typical application, a radiation delivery system has an ionizing radiation device mounted to a movable gantry. The radiation delivery system controls the motion of the radiation device to direct an ionizing radiation beam to a specific point in space commonly referred to as the “machine isocenter.” During radiation therapy, a patient is positioned so that the patient's tumor is located at the machine isocenter throughout treatment.
Radiation is typically delivered to a patient during a radiation therapy session in accordance with a session plan. A session plan typically specifies, for each of one or more “treatment fields,” such information as the gantry position, which determines the path that radiation energy will take to the tumor during the treatment field; collimator settings that determine the shape and cross-sectional area of the radiation energy beam; the intensity level of the radiation beam; and a duration that determines for how much time radiation energy will be delivered during the field. Various session plans may include different or additional information, however.
A plan is typically prepared using determinants such as the following: the tumor's mass, volume, shape, orientation, location in the body, and proximity to different organs and other anatomical structures; and information about radiation energy intended to be delivered to the tumor in foregoing radiation therapy sessions, as well as other approaches previously used to treat the tumor. Various plan preparation techniques may use fewer, more, or different determinants, however.
Conventionally, a batch of several session plans are prepared for a number of future sessions in advance of the sessions. In this batch approach to session plan preparation, the individual plans of the batch are often homogeneous, and assume either (1) no relevant changes in the patient's condition during the course of the batch, or (2) projected changes in the patient's condition determined in advance. This approach further typically assumes (1) that radiation has been and will be delivered in accordance with each plan with complete accuracy, or (2) that radiation has been and will be delivered in accordance with each plan at a projected level of accuracy determined in advance.
The batch approach to session plan preparation has the disadvantage that each plan of a batch after the first plan is based upon important assumptions that may in many cases be unwarranted. As a result, individual plans prepared using the batch approach may have various deficiencies, which have the effect of degrading the effectiveness of radiation therapy in treating the tumor.
In view the foregoing, and approach to session plan preparation having a reduced reliance on such important assumptions would have significant utility.